This application claims the benefit of Korean Application No. 10-2002-0073876 filed on Nov. 26, 2002, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to laundry dryers, and more particularly, to an apparatus for controlling a heater in a laundry dryer provided with a heater control interface for the control of a plurality of high voltages for driving the heater.
2. Discussion of the Related Art
In general, a laundry dryer is an apparatus for drying wet objects, e.g., clothes, after completion of a washing cycle or the like. FIG. 1 illustrates the circuit of a heater controller in a laundry dryer according to a related art.
Referring to FIG. 1, the heater control circuit is comprised of a microcomputer 10 for outputting a control signal according to a user input, a current buffer 20 for outputting a plurality of heater control signals based on the control signal of the microcomputer, and a heater drive unit 40 having a plurality of heater drivers for driving a heater 30 using one of a plurality of high voltages as determined by the heater control signals. Here, the plurality of high voltages is provided so that the heater 30 may be efficiently driven using a current appropriate for a given type of laundry according to a user selection. Typically, two such voltages are available for use in an ordinary household, and as a rule, these voltages are 110 volts and 220 volts. In other settings, such as an industrial or commercial environment, higher voltages may be additionally available.
The control signal of the microcomputer 10 is output via first and second ports S1 and S2, whose logic states determine the output of the current buffer 20. In the example of FIG. 1, the plurality of heater control signals includes first and second heater control signals H1 and H2 for respectively driving the heater 30 using a first high voltage, i.e., 110V, or a second high voltage, i.e., 220V. Accordingly, the heater drive unit 40 is comprised of first and second heater drivers 41 and 42, which essentially comprise first and second form A contact relays X1 and X2, respectively. The first and second heater drivers 41 and 42 are respectively connected to the first and second high voltages for driving, using one or the other voltage, the heater 30 according to the first and second heater control signals H1 and H2.
The first heater driver 41 includes a first diode D101 connected across the control terminals of the first relay X1 between a positive DC voltage source at its cathode and the H1 line at its anode, and a series connection of a first resistor R101 and a first capacitor C101 connected across the power terminals of the first relay between the first high voltage on the resistor side and the heater 30 on the capacitor side. Thus, when the first power control signal is low, current flows through the coil of the first relay X1, closing the relay switch and thus applying the first high voltage to the heater 30 via the enabled heater driver. Conversely, when the first heater control signal H1 is high, there is no current flow through the coil of the first relay X1, opening the relay switch so that the first high voltage is not applied to the heater 30.
Likewise, the second heater driver 42 includes a second diode D102 connected across the control terminals of the second relay X2, between a positive DC voltage source at its cathode and the H2 line at its anode, and a series connection of a second resistor R102 and a second capacitor C102 connected across the power terminals of the second relay, between the second high voltage on the resistor side and the heater 30 on the capacitor side. Thus, when the second heater control signal H2 is low, current flows through the coil of the second relay X2, closing the relay switch and thus applying the second high voltage to the heater 30 via the enabled heater driver. Conversely, when the second heater control signal H2 is high, there is no current flow through the coil of the second relay X2, opening the relay switch so that the second high voltage is not applied to the beater 30.
It should be appreciated that only one of the plurality of heater control signals output from the current buffer 20 is to be low at any given time. That is, while one heater control signal (e.g., H1) is low, all others (e.g., H2) should remain high.
Thus, if the current buffer 20 fails, the heater control signals will typically float high and both control terminals of each relay will therefore remain high, so that the relays remain open and no voltage is applied to the heater 30. As a result, the heater 30 cannot be driven, which is an inconvenience to the user but poses little danger. In the event of a microcomputer malfunction, however, there may be instances where the control signal output from the microcomputer 10 controls the current buffer 20 such that more than one heater control signal goes low, whereby the heater drive unit 40 would attempt to drive the heater 30 using multiple voltages, essentially shorting high-voltage lines together.
Therefore, the laundry drier according to the related art, in which the above-described heater control circuit is employed, may fail during operation and is potentially dangerous. That is, there may conditions where the heater cannot be driven, which renders the laundry drier wholly inoperative, and there may be conditions where a high-voltage short circuit is created, which may have catastrophic results.
Accordingly, the present invention is directed to a laundry dryer that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention, which has been devised to solve the foregoing problem, lies in providing a laundry dryer in which minimum dryer function is ensured and dangerous short-circuit conditions are prevented.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent to those having ordinary skill in the art upon examination of the following or may be learned from a practice of the invention. The objectives and other advantages of the invention will be realized and attained by the subject matter particularly pointed out in the specification and claims hereof as well as in the appended drawings.
To achieve these objects and other advantages in accordance with the present invention, as embodied and broadly described herein, there is provided a laundry dryer having a heater control circuit. The heater control circuit comprises a heater for being driven by a plurality of high voltages via a plurality of heater drivers; a microcomputer for outputting a control signal according to a user input, the control signal determining the high voltage drive is of the heater; and a heater control interface for generating a plurality of heater control signals corresponding to the plurality of high voltages, based on the control signal of the microcomputer, the plurality of heater control signals selectively enabling only one of the plurality of heater drivers.
It is to be understood that both the foregoing explanation and the following detailed description of the present invention are exemplary and illustrative and are intended to provide further explanation of the invention as claimed.